This invention relates to ink jets; and, more particularly, to ink jet recording systems utilizing a continuous stream of ink emitted from an orifice prior to droplet production.
Speed and versatility provided by non-impact printing processes have led to the development of several types. One type is referred to as ink jet printing and several forms of ink jet printing are known. One such form produces drops of ink upon demand and operates such that an ink filled cavity is deformed to squirt ink from the cavity, through the orifice and upon a receiving medium. In another form of ink jet printing, a meniscus of ink is maintained at the orifice and is drawn therefrom by electrostatic charge attraction upon a receiving medium. In another form of ink jet printing, magnetic ink is operated upon with magnetic field forces in addition to electrostatic field forces to cause deflection of the ink selectively into desired positions upon the receiving medium.
In the form of ink jet printing to which the present invention relates, conductive fluid is delivered under pressure through a cavity from which it exits through an orifice in the form of a continuous stream. Perturbation is applied to the ink in the cavity, such as for example, by periodic excitation of piezoelectric crystals mounted within the cavity, causing the continuous stream to break up into substantially uniform drops which are substantially uniformly spaced from one another. The point at which the continuous streams break up into droplets is herein referred to as the point of drop formation. At the point of drop formation, drop charge electrodes having a potential applied thereto induces a charge upon the drops. Selective deflection of the drops is then achieved by passing the drops through an electric field created by deflection electrodes having a voltage impressed thereon. The electric field created by the deflection electrodes operates upon the charged drop so as to selectively deflect the charged drop to a predetermined position on the receiving medium or to a gutter.
In the continuous stream form of drop formation in ink jet printing, the number of elements involved in selective deflection by deflection plates to either a gutter or to one of several locations on a print plane creates design problems. The requirement that these elements be located adjacent the path of flight of the ink between the orifice and the receiving medium; the burden of data processing required to be handled by the electronics in cases where the selective deflection by the deflection plates can be to either the gutter or the receiving member, and if to the receiving member then to any of a predetermined number of positions upon the receiving member; and the space required to be occupied by the number of elements along the ink flow path, provides design constraints which can affect the quality of printing, system cost, ease of fabrication, and packing density of nozzles within the drop generator. For example, the greater the number of elements required along the ink flow path between the point of drop formation and the receiving medium, the greater the resulting distance between the drop generator nozzles and the receiving medium; and, the greater the distance, the more accurate the sustem alignment and deflection parameters must be in order to hit the "target" of selected drop placement at the print plane.